(1) Field of the Invention
This invention relates to color photographic materials which provide a color image having good color reproduction and improved sharpness.
(2) Description of the Prior Art
The use of the interlayer restraining effect has been known as a useful means for improving color reproduction of color photographic materials. In color negative photographic materials, for instance, the development restraining effect from green-sensitive layers to red-sensitive layers may restrain color formation in the red-sensitive layer upon white light exposure to a greater extent than upon red light exposure. In a color negative film-color paper system, gradation is balanced so that an area exposed by white light reproduces neutral gray on a color print, and therefore the interlayer effect leads to greater cyan dye-formation in an area exposed by red light than in an area exposed by white light. As a result, the interlayer effect caused in the color negative film affords a color print of decreased cyan dye-formation, that is, reproducing highly saturated red color. Similarly, a development restraining effect from red-sensitive layers to green-sensitive layers leads to reproduction of green colors having higher saturation.
One method for increasing the interlayer effect so far known is a method using iodide ion released upon development from a silver halide emulsion. In this method, the silver iodide content of the donor layer of the interlayer effect is high, while the silver iodide content of the receptor layer is low. Another method for increasing the interlayer effect is, as described in Japanese Patent Application (OPI) (unexamined published application) No. 50-2537, one in which the donor layer of the interlayer effect includes a coupler which reacts with the oxidation products of a paraphenylenediamine type color developer to release a development restraining compound. Still another method for increasing the interlayer effect is one called an auto-masking method in which a colored coupler is incorporated in an uncolored coupler-containing layer to mask unwanted absorption of the colored dye produced upon development from the uncolored coupler. According to this method, it is possible to obtain a similar effect to the interlayer effect by increasing the amount of the colored coupler incorporated so that masking is effected to a greater extent than that necessary to mask the unwanted absorption of the colored dye produced from the uncolored coupler.
It is known that iodide ion which contributes to the development restraint and a development restrainer released from a development inhibitor-releasing (DIR) compound gives rise to not only the interlayer effect but also the Eberhard effect by diffusing also in the direction perpendicular to incident lights to improve image sharpness. As described in European Pat. No. 101,621 and Japanese Patent Application (OPI) No. 59-131934, the Eberhard effect is particularly remarkable if the development restrainer or its precursor has a high diffusibility. It is now becoming common in the field of photography to incorporate such DIR compounds into photographic materials to greatly increase the image shapness thereof.
In order to emphasize a contrast of fine lines at ten cycles per millimeter on a film by the Eberhard effect, it is necessary for the restrainer or its precursor to diffuse tens of microns during development, which is comparable to the total film thickness of the photographic materials swollen in the processing liquid. This means that the development restrainer would exert an effect on all the photographic layers of the photographic materials, which would cause the following adverse problems: In order to increase image sharpness, it is necessary to increase the diffusibility of the development restrainer or a precursor thereof. However, as the diffusibility becomes high, the interlayer development restraining effect also becomes high, which makes it difficult to control the direction and the extent of the development restraining effect. For example, if the DIR compound is incorporated into a blue-sensitive silver halide emulsion layer so as to have a desired interlayer effect from the blue-sensitive layer to a green-sensitive layer, the interlayer effect reaches also to a red-sensitive layer to such an extent that color reproduction becomes undesirable. It is therefore eagerly desired to solve the problem.
The inventors of the this invention have found that the incorporation of a DIR compound which releases a development restrainer having high diffusibility into a green-sensitive layer increases both the saturation of red color and the image sharpness of the green-sensitive layer which is the visually most important layer because the human eye has the highest sensitivity in the green region of the spectrum. They have also found that the incorporation of the DIR compound has a disadvantage in reproduction of green colors. Various green colors having different hue such as yellow-green, orange-green, cyan-green, brownish green, etc. which the human eye can discriminate, become colors of a cyan tint similar to each other on a color print which the human eye can no longer discriminate. They have studied and found the causes of such phenomenon as follows:
When the large interlayer effect is given from a green-sensitive layer to blue-sensitive and red-sensitive layers, the longer wavelength region of the spectral sensitivity distribution curve for the blue-sensitive layer and the shorter wavelength region of the spectral sensitivity distribution curve for the red-sensitive layer are made less sensitive by the interlayer effect as shown in FIG. 1, resulting in the substantial loss of the sensitivities of the blue-sensitive and the red-sensitive layers in the region of the spectrum which overlaps by the green-sensitive region. As a result, only the green-sensitive layer produces green dye but the blue-sensitive and the red-sensitive layers do not produce any color dye when the light sensitive materials are exposed to light having any wavelength within this green region. In other words, only the green-sensitive layer produces color dye when the interlayer effect from the green-sensitive layer is too large so as to completely inhibit the possible development in the blue-sensitive and/or the red-sensitive layers. This is the reason why green objects having different maximum absorption wavelength (.lambda.max) are liable to appear in a single green color as the color reproduced and consequently to worsen the discrimination of green colors having different hue.